It is usually known the use of control circuits in switching static regulators employed in power suppliers wherein particular features on the precision of the regulation are requested, as in the power supply circuits of the high performance modern microprocessors. Particularly such power suppliers must provide higher and higher currents and lower and lower voltages.
Switching regulators are used to perform said power suppliers. Each regulator comprises at least one MOS power transistor; particularly some regulators comprise a pair of MOS transistors or several pairs of MOS transistors which are arranged in parallel to each others and which are connected with a single output terminal by means of an inductance for each transistor pair (Multi-phase converters). The output currents of said pairs of transistors are automatically balanced by means of a control operation which detects each single current by detecting the voltage drop between the drain and source terminals of the MOS transistor. This voltage drop is also employed for implementing a well precise and programmable load regulation as a function of the current provided to the load, as it is required from particular loads such as the microprocessors.
It is however known that the MOS transistors are provided internally of a resistance between the drain and source terminals in the conduction or firing phase, known as on or conduction resistance Rdson, which changes with the temperature and which, for this reason, can cause variations of the voltage signal between the drain and source terminals of the MOS transistor with currents of the same value. This occurs above all in the power MOS transistors because the current flowing through the source and drain terminals thereof is high and consequently the variation of the voltage drop at the terminals of the MOS transistor which is due to the thermal variation of the on resistance, is also high above all in the cases wherein, for size problems, thermal dissipators or fans are not used.
Therefore the thermal variation of the on resistance (Rdson) of the MOS may cause very high variations of the voltage regulated by the power suppliers which employ the voltage detected between the terminals of the MOS transistor for regulating the output voltage on the load to be supplied. This may bring to non-respect of some specifications of the loads such as the microprocessors.
A possibility to avoid the variations of the voltage detected between the terminals of the MOS transistor of the voltage regulators consists of adding and consequently using measurement elements that are substantially invariant in temperature, for example resistors known as “sense resistors”. The signal measured between the terminals of the sense resistors acts in the control operation of the MOS transistor for regulating suitably the output voltage of the regulator. Such resistors have thermal variations lower than the resistance Rdson, are very precise but the high precision thereof is compromised by the high contact resistance due to the welding thereof on the printed circuit of the regulator. Also the power dissipated by the sense resistors decreases the effectiveness of all the regulator and the use thereof causes a higher cost of all the appliance.
In view of the art described, it is an object of the present invention to provide a switching voltage regulator that overcomes the aforementioned disadvantages.